Methods, Catalysts, and Supports for Electrochemical Devices

ABSTRACT

Embodiments described herein relate to methods for preparing catalysts and catalyst supports. In one embodiment, transition metal carbide materials, having a nanotube like morphology, are utilized as a support for a precious metal catalyst, such as platinum. Embodiments described herein also relate to proton exchange membrane fuel cells that incorporate the catalysts described herein.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. Provisional Patent ApplicationNo. 62/307,450, filed Mar. 12, 2016, the entirety of which is hereinincorporated by reference.

BACKGROUND

Field

Embodiments of the present disclosure generally relate to improvedcatalysts for fuel cells. More specifically, embodiments describedherein relate to methods, catalysts, and supports for fuel cells andother catalytic systems.

Description of the Related Art

Transition metal carbides (TMCs) have been a popular research area dueto their similar electronic and geometric structure to platinum (Pt) andPt group metals. TMCs are not only an order of magnitude less expensiveand more abundant than Pt group metals, but have also shown Pt-likecatalytic performance in hydrogenation, dehydrogenation andhydrogenolysis. These metal carbides could be an alternative to Pt inhydrogen evolution reactions (HER), hydrogen oxidation (HOR)applications, or oxygen reduction reactions (ORR). However, despiterecent advances in carbide research, electrocatalytic activity of group4 and 6 TMCs are still not comparable to conventional catalysts, such asPt supported on carbon black (Pt/C).

Accordingly, what is needed in the art are improved supports andcatalysts for various catalytic application.

SUMMARY

In one embodiment, a catalyst formation is provided. The method includespreparing a mixture comprising one or more halide slats, multi-walledcarbon nanotubes, and a transition metal, heating the mixture to atemperature greater than about 900° C. to form a transition metalcarbide support, boiling and rinsing the transition metal carbidesupport to remove excess salts, and drying the transition metal carbidesupport. The method also includes depositing platinum on the transitionmetal carbide support, wherein the depositing comprises atomic layerdeposition (ALD) of platinum nanoparticles utilizing a platinumprecursor and an oxygen precursor in a rotating ALD reactor.

In another embodiment, a catalyst formation method is provided. Themethod includes preparing a mixture comprising one or more halide salts,multi-walled carbon nanotubes (MWCNTs) and a transition metal. A ratioof halide salts:MWCNTs:transition metal is about 67:7:26. The mixture isheated to a temperature greater than about 900° C. to form a transitionmetal carbide support, the transition metal carbide support is boiledand rinsed to remove excess salts, and the transition metal carbidesupport is dried. The method also includes depositing platinum on thetransition metal carbide support, wherein the depositing comprisesatomic layer deposition (ALD) of platinum nanoparticles in a rotatingALD reactor and the number of ALD cycles is between about 15 and about100.

In yet another embodiment, a fuel cell apparatus is provided. Theapparatus includes a proton exchange membrane, a first catalystcomprising platinum molybdenum carbide disposed on a first side of theproton exchange membrane and a second catalyst comprising platinummolybdenum carbide disposed on a second side of the proton exchangemembrane opposite the first catalyst. The first and second catalysts arephase pure and the platinum is formed as discrete nanoparticles on themolybdenum carbide. The apparatus further includes a first gas diffusionlayer disposed on the first side of the proton exchange membrane and thefirst catalyst is disposed between the first gas diffusion layer and theproton exchange membrane. A second gas diffusion layer is disposed onthe second side of the proton exchange membrane and the second catalystis disposed between the second gas diffusion layer and the protonexchange membrane. An anode is coupled to the first gas diffusion layerand a cathode is coupled to the second gas diffusion layer.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentdisclosure can be understood in detail, a more particular description ofthe disclosure, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlyexemplary embodiments and are therefore not to be considered limiting ofits scope, may admit to other equally effective embodiments.

FIG. 1 illustrates a cross-sectional, schematic view of a fuel cell 100according to embodiments described herein.

FIG. 2 illustrates x-ray diffraction of bare Mo2C and MWCNTs (inset)according to embodiments described herein.

FIG. 3(a) illustrates a high resolution transmission electronspectroscopy (HRTEM) image of a bare Mo₂C (100) nanotube with latticespacing according to embodiments described herein.

FIG. 3(b) illustrates an HRTEM image of 15 Pt/Mo₂C according toembodiments described herein.

FIG. 3(c) illustrates a close up of the image of FIG. 3(b) according toembodiments described herein.

FIG. 3(d) illustrated an HRTEM image of 50 Pt/Mo₂C according toembodiments described herein.

FIG. 3(e) illustrates an HRTEM image of 100 Pt/Mo₂C according toembodiments described herein.

FIG. 4(a) illustrates lattice fringe analysis of HRTEM images of 50Pt/Mo₂C according to embodiments described herein.

FIG. 4(b) illustrates lattice fringe analysis of HRTEM images of 100Pt/Mo₂C according to embodiments described herein.

FIGS. 4(c) and 4(d) illustrate the inverse fourier transform of FIG.4(b) according to embodiments described herein.

FIG. 5(a) illustrates XPS data of bare Mo₂C, 15 Pt/Mo₂C, 50 Pt/Mo₂C, and100 Pt/Mo₂C according to embodiments described herein.

FIG. 5(b) illustrates a detailed view of the Pt 4f spectra of FIG. 5(a)and the inset of FIG. 5(b) is the binding energy shift vs. number of ALDcycles according to embodiments described herein.

FIG. 6(a) illustrates linear sweep voltammograms (LSV) of 100 Pt/Mo₂C,50 Pt/Mo₂C, 15 Pt/Mo₂C, 20% Pt/C, and Mo₂C according to embodimentsdescribed herein.

FIG. 6(b) illustrates the LSV of 100 Pt/Mo₂C, 50 Pt/Mo₂C, and 20% Pt/Cper mass of Pt and normalized current per Pt mass at −144 mV vs RHE isshown in the inset of FIG. 6(b) according to embodiments describedherein.

FIG. 6(c) illustrates Tafel plots of the materials of FIG. 6(a) usingthe LSV data shown in FIG. 6(a) according to embodiments describedherein.

FIG. 7(a) illustrates cyclic voltammograms (CV) of 15 Pt/Mo₂C and bareMo₂C according to embodiments described herein.

FIG. 7(b) illustrates cyclic voltammograms of 50 Pt/Mo₂C, 100 Pt/Mo₂C,Pt/Mo₂C, and 20% Pt/C according to embodiments described herein.

FIG. 8(a) illustrates durability tests with LSVs of 100 Pt/Mo₂Caccording to embodiments described herein.

FIG. 8(b) illustrates durability tests with LSVs of 50 PT/Mo₂C accordingto embodiments described herein.

FIG. 8(c) illustrates durability tests with LSVs of 20% Pt/C accordingto embodiments described herein.

FIG. 8(d) illustrates 15 Pt/Mo₂C including the LSV after 3000 potentialcycles according to embodiments described herein.

FIG. 8(e) illustrates a graphical comparison of current density changefor each of catalysts 20% Pt/C, 100 Pt/Mo₂C, 50 Pt/Mo₂C, and 15 Pt/Mo₂Caccording to embodiments described herein.

FIGS. 9(a)-(c) illustrate polarization and power density curve data ofmembrane electrode assemblies fabricated with 100 Pt/Mo₂C and 20% Pt/Caccording to embodiments described herein.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements and features of oneembodiment may be beneficially incorporated in other embodiments withoutfurther recitation.

DETAILED DESCRIPTION

Embodiments described herein provide for nanoscale TMCs having improvedsupport surface area with atomic level control of deposited Pt particleswhich are believed to provide synergetic effects of a Pt-TMC catalystplatform. Generally, vapor phase deposition, such as atomic layerdeposition (ALD), offers control in the resulting Pt particle size anddispersion and, ultimately, increased catalyst activities. For example,ALD provides suitable control of deposited particles, on the molecularor atomic level, by tuning process parameters such as number of ALDcycles, as a result of sequential, self-limiting surface reactions.

For Pt ALD processes, it is believed that the island growth mechanismdominates the initial tens to hundreds of cycles due to stronger bondingbetween Pt atoms than bonding between Pt and other substrate surfaces.Embodiments described herein provide for ALD deposition of Ptnanoparticles onto phase-pure Mo₂C nanotubes that are synthesized viasalt-flux method (10-15 nanometers in diameter, 1-2 microns in length).Embodiments also provide for tuning Pt nanoparticle size from atomic toabout 3 nm via ALD. The Pt/Mo₂C nanocatalyst platform, among othersdescribed herein, is believed to provide for improved catalytic activityresulting from the synergetic effect of TMC supports for precious groupmetal (PGM) catalysts, such as platinum or the like. Pt ALD modifiedMo₂C nanotubes (referred to hereinafter as Pt/Mo₂C) are also describedwith regard to utilization in a proton exchange membrane fuel cell(PEMFC).

EXPERIMENTAL Synthesis of Metal Carbides

In one embodiment, Mo₂C nanotubes were synthesized via a salt fluxapproach. In this embodiment, 0.13 g of sodium chloride, 0.37 g ofsodium fluoride, 0.05 g of multi-walled carbon nanotube (MWCNT), and0.20 g of molybdenum powder (Sigma-Aldrich) were ground in a mortar. Inone embodiment, the halide salts (NaCl and NaF), the MWCNTs, and thetransition metal (molybdenum) are present in the mixture in a ratio ofabout 67:7:26, respectively.

Then, the mixture was placed in a crucible and moved to a tubularfurnace. The furnace temperature was ramped to a temperature greaterthan 900° C. and heated at the temperature for a period of time ofgreater than about 10 hours. In one embodiment, the mixture was heatedto a temperature of about 975° C. over a duration of 9.75 hours,stabilized at about 975° C. for about 14 hours, and then cooled to roomtemperature. While in the furnace, the mixture was kept in an inertenvironment. In one embodiment, the mixture is maintained in a flowingArgon environment. After the furnace temperature reached roomtemperature, the powder was removed and excessive salts were washed awayby boiling and rinsing the mixture in deionized water. Finally, the Mo₂Cpowder was dried in air at a temperature of between about 25° C. andabout 100° C., such as about 50° C. for a period of time between about 8hours and about 16 hours. The resulting molybdenum carbide supportformed according to the embodiments described about is phase pure andhas a nanotube morphology. In one embodiment, the molybdenum carbidesupport nanotubes have a length of between about 1 micron and about 2microns and a diameter of between about 10 nm and about 15 nm.

Pt was deposited onto molybdenum carbide via ALD using Platinum (IV)Trimethyl (methylcyclopentadienyl) (MeCpPtMe₃) as the platinum precursorand oxygen as the oxidant. In one embodiment, 15 Pt ALD cycles wereutilized. In this embodiment, the resulting catalyst is referred to as15 Pt/Mo₂C. In another embodiment, 50 Pt ALD cycles were utilized. Inthis embodiment, the resulting catalyst is referred to as 50 Pt/Mo₂C. Inanother embodiment, 100 Pt ALD cycles were utilized. In this embodiment,the resulting catalyst is referred to as 100 Pt/Mo₂C. The reactions werecarried out in a rotating ALD reactor and the deposition temperature wasmaintained between about 100° C. and about 300° C., such as about 200°C., during deposition of the Pt on the Mo₂C support.

Generally, the rotating ALD reactor design is based on two concentriccylinders. The outer cylinder remains fixed and contains a series ofslits. The slits can accept a wide range of modules that attach from theoutside. The modules can easily move between the various slit positionsand perform precursor dosing, purging, or pumping. The inner cylinderrotates with the substrate (Mo₂C support) and passes underneath thevarious spatially separated slits in the outer cylinder.

While the above referenced embodiments, in addition to subsequentcharacterization and results, relate to the Pt/Mo₂C catalyst platform,other and further catalyst platforms are contemplated. For example,improved salt flux techniques reduce reaction temperatures and can beutilized to form catalyst support materials in the nanometer regime. Inaddition, utilization of MWCNTs as a reactant is believed to furtherreduce diffusion distance and also provides a template for theultimately formed carbide materials. Accordingly, metal carbidecompounds produced utilizing low temperature salt flux techniques canmaintain the nanowire morphology of the carbon nanotubes but increase insize to between about 15 nm and about 20 nm in diameter due to theincorporation of metal in the carbon lattice. The nano-carbides formedaccording to methodologies described hereinafter not only have ananowire like shape but also have increased surface areas when comparedto conventionally prepared metal carbides. Moreover, bimetallic carbidesmay be produced by utilizing two metal precursors in the salt fluxreaction. Thus, it is contemplated that methods described herein providefor nano sized metal carbide materials with controllablecharacteristics, such as size, morphology, and composition.

In various examples, MWCNT's (<95% and average 6.6 nm diameter) may bemixed with a metal powder selected from one or more of chromium (99.5%),molybdenum (99.9%), tungsten (99.9%), vanadium (99.5%), niobium (99.8%)tantalum (99.9%), titanium (99.7%), zirconium (<99%), and hafnium(99.5%), all of which are commercially available from Sigma Aldrich. TheMWCNT's and desired metal powder may be mixed with a LiCl—KCl—KF flux(LiCl:KCl:KF=58:41:1 wt %) in a glovebox, or other controlledenvironment apparatus, to limit exposure to oxidizing materials, such asoxygen. The mixture is then heated in an alumina boat at a temperaturebetween about 400° C. and about 1050° C. for an amount of time betweenabout 5 hours and about 12 hours in an Argon purged atmosphere. Oncecooled, the mixture may be washed with water to dissolve the salt fluxout of the reaction product. The resulting carbide reaction product maythen be optionally centrifuged and dried.

More specifically, the carbide synthesis utilizes a molten salt flux asa reaction medium which is suitable for all group 4-6 metals. Tosynthesize carbide nanowires, a eutectic mixture of KCl and LiCl may beground together with a mixture of MWCNTs and bulk metal powders. Thecombination of halide salts (KCl and LiCl) forms a molten/liquidreaction medium at low temperatures (e.g. below about 400° C.). KF saltsmay also be utilized in an amount of between about 1 wt % and about 5 wt% of the reaction medium to improve the reaction rate in certainembodiments. For all reactions, the ratio of metal to carbon isstoichiometric except for the tungsten and chromium systems whereadditional carbon is utilized. While single metal carbides are discussedin detail below, bimetallic metal carbides may also be formed byutilizing two metal powders in the reaction mixture. In this embodiment,the alloy composition of the bimetallic metal carbide may be controlledto form materials having desirable characteristics, such as improvedsurface area and the like. In another embodiment, trimetallic metalcarbides may also be formed bu utilizing three metal powders in thereaction mixture. Similar to the bimetallic metal carbide materials, analloy composition of the trimetallic metal carbide may be controlled toform materials having desirable characteristics.

TABLE 1 Metal Temp (° C.) Time (hr) Carbon:metal Phase formed Titanium400-900 5 1:1 TiC Vanadium 600-950 5 1:1 V₈C₇ Chromium 950 5 1:1 Cr₃C₂Zirconium 850 5 1:1 ZrC Niobium 800-950 5 1:1 Nb₄C₃ Niobium 950 12 1:1NbC Molybdenum 950 12 1:2 Mo₂C Hafnium 750-950 5 1:1 HfC Tantalum750-950 5 1:1 TaC Tungsten 1050  12 3:1 WC

Table 1 illustrates synthesis conditions utilized for single metalcarbides formed utilizing the above described methods. Phases for eachof the resulting metal carbides were determined by powder x-raydiffraction (XRD). TiC and TaC adopted the NaCl structure and had thefollowing lattice constants a=4.137 Å and a=4.454 Å, respectively. Nb₄C₃and V₈C₇ obtained ordered non-stoichiometric phases but both stillpossessed the NaCl parent structure with lattice constants of a=4.445 Åand a=8.330 Å, respectively. VC_(1-x) is not stable with carbon contentover VC_(0.88) but forms an ordered phase with cubic symmetry at V₈C₇.When using a 1:1 ratio of metal to carbon, Nb₄C₃ forms but upon heatingfor 12 hr as opposed to 5 hr, the stoichiometric phase can be formed. Aslight excess of carbon (1:1.1) can also force the reaction toward thestoichiometric phase. The lattice constant for NbC is a=4.47 Å, but isotherwise substantially identical to the non-stoichiometric phase. ZrCand HfC are also stoichiometric phases that adopt the NaCl structure.

Cr₃C₂ is an orthorhombic phase with lattice constants a=11.47 Å, b=5.53Å, and c=2.82 Å and is less symmetric than the NaCl type structureobserved for other carbides. In this phase, the metal atoms are notclose packed and instead form edge sharing trigonal prisms with carbonat the center of the prism. WC also formed a non-NaCl type hexagonalstructure where the W and C atoms form layered hexagonal substructures.

The nanotubes of the various carbide materials are believed to grow indiameter upon conversion from carbon to carbide with average diametersbetween about 15 nm and about 20 nm. It is believed that the nanowiresvary in size and shape as a result of the different crystal structuresand reaction temperatures, however, the overall morphology between allthe carbides is substantially maintained. In addition, the wire-likemorphology and interwoven nature of the carbides provide for multipleredundant electronic connections while still providing high surface areawhich is ideal for catalysis. For example, Brunauer-Emmet-Teller (BET)surface area measurements for the product carbides range from about 10M² g⁻¹ to about 50 m² g⁻¹, while carbides formed from traditionalsynthesis methods typically result in BET surface areas below about 5 m²g⁻¹.

Materials Characterization

Referring back to the Pt/Mo₂C catalyst, the phases present in eachsample (15, 50, 100) were determined by XRD using a Rigaku Smart LabX-ray diffractometer (XRD) with Cu Kα radiation (A=1.54060 Å). Thed-spacings measured from XRD patterns were compared to the database ofinorganic compound powders PDF2 to identify the crystalline phasespresent. X-ray photo spectroscopy (XPS) was carried out using a KratosAxis Ultra DLD XPS with a monochromated Al K-alpha source under 10⁻¹⁰torr vacuum. Survey scans were performed at 80 eV pass energy with anenergy resolution of 0.5 eV and 3 sweeps. High resolution scans wereperformed at 40 eV pass energy with an energy resolution of 0.02 eV and3 sweeps.

Pt mass loading was measured using atomic absorption spectroscopy (AAS)and inductively coupled plasma optical emission spectrometry (ICP-OES)techniques (when detectable). AAS was carried out by a Perkin Elmer AASinstrument. Flame technique was used with a wavelength of 265.95 nm,slit width of 0.7 nm, lamp current of 30 A, and 75 eV of energy.Calibration was performed using a zero intercept nonlinear model.Unknown sample solution for AAS was prepared by dissolving 50 mg ofPt/Mo₂C in 3.5 ml aqua regia (HNO₃:HCl=1:3). 1000 mg/L Pt in 5% HCl(commercially available from Sigma-Aldrich) was used for calibration.ICP-OES analysis was performed to further quantify the amount of Ptdeposited on Mo₂C from various numbers of ALD cycles by using a PerkinElmer Optima 8300 instrument equipped with Perkin Elmer S10 auto samplerand WinLab 32 software. Samples for ICP-OES were prepared the same wayas for AAS. Pt ICP standard (1000 ppm in 5 wt % HCl) was obtained fromFluka. 265.95 nm and 214.42 nm detection wavelengths were chosen for Pt.

High resolution transmission electron microscopy (HRTEM) was used tocharacterize the morphology and Pt distribution on the carbide nanotubesunder bright field (BF) mode with an FEI Tecnai F2 G20 S-Twin (S)TEMwith an accelerating voltage of 200 kV. Pt nanoparticle size wascalculated using ImageJ. BET (Brunauer-Emmett-Teller) surface area wasmeasured by nitrogen physisorption at 77 K using a Micromeritics APAP2020 with surface area analyzer.

Electrochemical Tests

Using a three-electrode system, cyclic voltammetry (CV) and linear sweepvoltammetry (LSV) measurements were carried out in N₂ saturated 0.5MH₂SO₄ (pH=0) solution to evaluate the oxidation stability, HER activityof the Mo₂C and Pt/Mo₂C catalysts. As a baseline comparison, CV and LSVwere also collected for commercial 20% Pt supported on a vulcan XC-72(Johnson Matthey) catalyst under the same conditions (referred to as 20%Pt/C hereafter). Glassy carbon (3 mm diameter) was used as workingelectrode, with Pt wire as a counter electrode and Ag/AgCl saturated in3 M NaCl as a reference electrode.

Catalyst ink was prepared by ultrasonically suspending 5 mg of catalystin 2 mL of ethanol and 50 μL of 5 wt % Nafion® solution for 15 min. 10μL of the suspended catalyst was spread on the working electrode anddried to obtain a thin active layer (with a loading of 0.35 mg catalystcm⁻² on the disk). Potential was applied between the reference and thecounter electrode while the current was measured between the counter andthe working electrode via CompactStat e10800 potentiostat (commerciallyavailable from Ivium Technology). The 0.5M H₂SO₄ electrolyte solutionwas purged with N₂ for one hour prior to electrochemical testing. N₂flow (0.2 L/min) was maintained above the electrolyte throughout thetesting to eliminate O₂ from the environment.

Durability testing was carried out by constant potential electrolysis(CPE) at −69 mV vs. RHE for 48 hours in 0.1M HClO₄ (pH=1), followed bypotential cycling between −0.4 to 0.6V for 3000 cycles. Prior to CPEexperiments, the electrolyte was purged with N₂ for 20 minutes. Catalystink for durability testing was prepared by sonicating 2.5 mg catalyst in312.5 mL (18.2 MΩ ultrapure) water and 62.5 μL 5 wt % Nafion® solution(commercially available from Sigma Aldrich) for 30 minutes. Theelectrode was then dried at 50° C. for two hours.

Fuel Cell Fabrication and Testing

Membrane electrode assemblies (MEAs) were fabricated using ionomers, forexample, sulfonated tetrafluoroethylene based co-polymer materials. Oneexample of a suitable ionomer is Nafion® 212 (commercially availablefrom DuPont). In one embodiment, the Nafion® 212 membrane was firstboiled in 3% H₂O₂ for one hour, followed by one hour of boiling indeionized (DI) water, then one hour of boiling in 1 M H₂SO₄, and finallyone hour of boiling in DI water. Carbon based macro and micro porousmaterials were utilized as a gas diffusion layer (GDL). In oneembodiment, a SIGRACET® 10 BC carbon paper (commercially available fromIon Power) was used as a Gas Diffusion Layer (GDL). Catalyst inks wereprepared by combining the desired catalyst, methanol (for 20% Pt/C) orethanol (for Pt/Mo₂C), and Nafion® solution. 5% Nafion® ionomer solution(commercially available from DuPont) was added such that the Nafion®solids were 30% of the total mass of catalysts and Nafion® solids in theink. An alcohol, such as methanol or ethanol, was added in an amountthat was ten times the mass of catalyst in the ink. The ink was thensonicated for 20 minutes.

The gas diffusion electrode was prepared by painting the GDL, however,other catalyst application techniques are contemplated. The catalystloading on the GDL was determined by measuring the weight of the emptyGDL and the weight after depositing catalyst on the GDL by amicrobalance (commercially available from Sartorius). The membrane withgas diffusion electrode on both sides was pressed using digital combomulti-purpose heat press (DC14, commercially available from GEO Knight &Co. Inc.). The pressing condition was maintained at 135° C. at 80 psigfor 5 minutes. The MEA was tested using a fuel cell testing station(commercially available from Scribner Associates, Inc.) at 80° C. H₂ andO₂ flowrates were maintained at 0.2 liter/min with relative humidity of100% for both gas streams. Before starting each polarization experiment,MEAs were conditioned by humidification at 80° C. for 3 hours, followedby holding the potential at 0.6 V for one hour. Sequentially, potentialwas altered between 0.7 and 0.5V (holding at each voltage for twentyminutes) for the total duration of twelve hours then holding at currentof 1 ampere (A) for seven hours. The polarization experiments wereperformed with 100 Pt/Mo₂C and 20% Pt/C on the anode side, while keeping20% Pt/C on the cathode with Pt loading of 0.4 mg Pt cm⁻².

FIG. 1 illustrates a cross-sectional, schematic view of a fuel cell 100according to embodiments described herein. In one embodiment, the fuelcell 100 is a PEMFC type fuel cell. The fuel cell 100 includes a protonexchange membrane 102, a first catalyst material layer 104 disposed onthe proton exchange membrane 102, and a second catalyst material layer106 disposed on the proton exchange membrane 102 opposite the firstcatalyst material layer 104. In one embodiment, the proton exchangemembrane 102 is a sulfonated tetrafluoroethylene based co-polymermaterial, such as Nafion®.

The first catalyst material layer 104 and the second catalyst materiallayer 106 are disposed on opposite sides of the proton exchange membrane102 by various application techniques, such as painting, stamping,immersion, or the like. In one embodiment, the catalyst material layers104, 106 is the Pt/Mo₂C materials described herein, such as the 15Pt/Mo₂C, the 50 Pt/Mo₂C, or the 100 Pt/Mo₂C. It is also contemplatedthat other catalyst materials, such as transition metal carbides, mayalso be utilized for the catalyst material layers 104, 106. Suitableexamples of such materials include TiC, V₈C₇, Cr₃, C₂, ZrC, Nb₄C₂, NbC,HfC, TaC, WC, and combinations thereof. Each of the aforementionedmaterials may be formed according to the methods described herein.

A first gas diffusion layer 108 is coupled to the proton exchangemembrane 102 such that the first catalyst material layer 104 is disposedbetween the proton exchange membrane 102 and the first gas diffusionlayer 108. A second gas diffusion layer 110 is coupled to the protonexchange membrane 102 such that the second catalyst material layer 106is disposed between the proton exchange membrane 102 and the second gasdiffusion layer 110. In one embodiment, the gas diffusion layers 108,110 may be carbon based macro and/or micro porous materials, such asSIGRACET® 10 BC.

An anode 112 is coupled to the first gas diffusion layer 108 oppositethe proton exchange membrane 102 and the first catalyst material layer104. A cathode 114 is coupled to the second gas diffusion layer 110opposite the proton exchange membrane 102 and the second catalystmaterial layer 106. In one embodiment, the anode 112 and the cathode 114are formed from conductive materials, such as metallic materials andgraphite material or the like.

In operation, hydrogen fuel is delivered to and flowed through a flowchannel 116 adjacent the anode 112. An oxidant (oxygen or air) isdelivered to and flowed through a flow channel 118 adjacent the cathode114. At the anode 112, the hydrogen traverses the first gas diffusionlayer 108 and the first catalyst material layer 104 causes the hydrogento split into positive hydrogen ions (protons) and negatively chargedelectrons.

The proton exchange membrane 102 allows the positively charged ions topass through toward the cathode 114. The negatively charged electronsare rejected by the proton exchange membrane 102 and travel along acircuit 120 to the cathode 114, creating an electrical current. At thecathode 114, the electrons and positively charged hydrogen ions combinewith oxygen to form water which flows out of the fuel cell 100.

Results

Characterization of Mo₂C and Pt/Mo₂C Nanotube and Pt Quantification

FIG. 2 illustrates x-ray diffraction of bare Mo2C and MWCNTs (inset)according to embodiments described herein. The X-ray diffraction (XRD)pattern of bare Mo₂C samples showed peak positions and relativeintensity accurately corresponding to hexagonal Mo₂C (also referred asβ-Mo₂C). Comparison between the XRD patterns of MWCNTs (FIG. 2 inset)and Mo₂C indicates the amount of unreacted MWCNTs (if present) is beyondthe typical detection limit for XRD (˜2%). It should also be mentionedthat no significant peak from unreacted Mo was observed. In addition, itis noted that the starting materials for ALD deposition processes arephase-pure β-Mo₂C. As such, there is less than 6.4% amorphous carbon inall Mo₂C samples used for Pt ALD.

XRD of 100 Pt/Mo₂C shows no extra peak related to Pt crystalline phaseindicating Pt crystalline dimension is beyond the typical detectionlimit for XRD. However, a slight peak shift was observed for the Mo₂Cpeaks, implying deposition of Pt nanoparticles indeed changed thelattice constants of Mo₂C support.

FIG. 3(a) illustrates a high resolution transmission electronspectroscopy (HRTEM) image of a bare Mo₂C (100) nanotube with latticespacing. The lattice fringes of Mo₂C are in the direction of (100) planewith spacing of 0.26 nm. FIG. 3(b) illustrates an HRTEM image of 15Pt/Mo₂C. FIG. 3(c) illustrates a close up of the image of FIG. 3(b).FIG. 3(d) illustrated an HRTEM image of 50 Pt/Mo₂C. FIG. 3(e)illustrates an HRTEM image of 100 Pt/Mo₂C.

Different numbers of ALD cycles resulted in the desired island growthmechanism of Pt with a narrow distribution of particle sizes (FIG. 3(b), (c), (d) and (e)). For the 15 Pt/Mo₂C sample, Pt particles werebarely discernible on the nanotube (FIGS. 3(b) and 3(c)). In contrast,samples of 50 and 100 Pt/Mo₂C showed significantly increasednanoparticle density and size, with most Pt particle sizes being 1.5 nmand 2.5 nm for 50 Pt/Mo₂C and 100 Pt/Mo₂C, respectively (FIGS. 3(d) and3(e)). It should be noted that the atomic radius of Pt is about 0.135nm.

FIG. 4(a) illustrates lattice fringe analysis of HRTEM images of 50Pt/Mo₂C. FIG. 4(b) illustrates lattice fringe analysis of HRTEM imagesof 100 Pt/Mo₂C. FIGS. 4(c) and 4(d) illustrate the inverse fouriertransform of FIG. 4(b). The lattice fringe analysis in FIG. 4(a)illustrates that the lattice spacing inside a relatively bigger Ptparticle is around 0.21 nm for 50 Pt/Mo₂C samples, which corresponds tothe inter planar distance of Pt (111), while it is 0.24 nm for smallerparticles. Interestingly, for 100 Pt/Mo₂C samples in particles withsizes ranging 3-4 nm it can be seen that lattice spacing increaseswithin one particle from the center to edge (FIG. 4(b)).

Using inverse fourier transform, the lattice spacing is found to be 0.21nm near the center (FIG. 4(c)) and 0.24 nm near the edges of Ptparticles (FIG. 4(d)). With the lattice spacing of bare Mo₂C nanotube at0.26 nm (FIG. 3(a)) and that of Pt (111) being 0.21 nm, it is believedthat the Pt lattice was more stretched for smaller Pt nanoparticles andnear the edge, possibly due to stronger interaction between Pt and Mo₂Clattices. As Pt particles grow in both horizontal and verticaldirection, the strain between the Pt lattice on the top and Mo₂C supportdecreases, resulting in lattice spacing of 0.21 nm near the center ofbigger Pt particles.

FIG. 5(a) illustrates XPS data of bare Mo₂C, 15 Pt/Mo₂C, 50 Pt/Mo₂C, and100 Pt/Mo₂C. FIG. 5(b) is a detailed view of the Pt 4f spectra of FIG.5(a) and the inset of FIG. 5(b) is the binding energy shift vs. numberof ALD cycles. Further surface characterization using XPS confirmed thepresence of Pt on all ALD modified Pt/Mo₂C samples. The binding energies(BE) were calibrated against C1S (284.5 eV). Shown in FIG. 5(b) are thehigh-resolution XPS of Pt 4f spectra indicating a binding energy shiftbetween Pt particles and Mo₂C nanotube support and, consequently,electron transfer from Pt to Mo₂C. For 100 Pt/Mo₂C samples, the BEshifted about 0.5 eV from Pt⁰ state, while 0.74 and 1.0 eV shifts fromPt⁰ were observed for 15 and 50 Pt/Mo₂C samples, respectively.

In other words, BE shift with increasing particle size has a volcanoprofile (FIG. 5(b) inset). BE shift decrease from 50 Pt/Mo₂C to 100Pt/Mo₂C as Pt particle size increased apparent, even with particle sizessmaller than 2 nm. The volcano profile of BE shift vs particle size isalso observed when particle size of 100 Pt/Mo₂C was reduced with time bytemporal argon depth profiling on 100 Pt/Mo₂C. The volcano profileobserved in three discrete Pt/Mo₂C samples of different sizes and thetemporal particle size decrease suggest that particle size isinfluential for BE shift.

Electrochemical Characterization of Pt/Mo₂C

To probe activity of the Pt/Mo₂C samples on the basis of Pt massloading, a mass percentage of Pt in 50 Pt/Mo₂C and 100 Pt/Mo₂C samplesfrom the MeCpPtMe₃/O₂ precursor system were quantified by AAS andICP-OES and summarized in Table 2.

TABLE 2 Sample Pt wt % by ICP-OES Pt wt % by AAS 100 ALD cycle Pt/Mo₂C 4.4% 3.67%  50 ALD cycle Pt/Mo₂C 1.07% —

FIG. 6(a) illustrates linear sweep voltammograms (LSV) of 100 Pt/Mo₂C(15.4 μg Pt cm⁻² _(disk)), 50 Pt/Mo₂C (3.75 μg Pt cm⁻² _(disk)), 15Pt/Mo₂C (Pt loading was below detection limit of ICP or AAS), 20% Pt/C(70 μg Pt cm⁻² _(disk)), and Mo₂C with a scan rate of 2 mV s⁻¹ in N₂saturated H₂SO₄ solution. FIG. 6(b) illustrates the LSV of 100 Pt/Mo₂C,50 Pt/Mo₂C, and 20% Pt/C per mass of Pt. Normalized current per Pt massat −144 mV vs RHE is shown in the inset of FIG. 6(b). FIG. 6(c)illustrates Tafel plots of the materials of FIG. 6(a) using the LSV datashown in FIG. 6(a).

Linear sweep voltammetry (LSV) was performed to characterize the HERactivity of Pt/Mo₂C catalysts fabricated using different numbers of ALDcycles. The HER onset potential was calculated using tangents of the LSVcurves (FIG. 6(a)). Table 2 summarizes the onset potentials for all thesamples. Comparison among the catalysts revealed that the onsetpotential for bare Mo₂C nanotubes (−0.32 V vs. RHE) is significantlyhigher than all the Pt/Mo₂C samples. HER activity increased with theincrease in number of Pt ALD cycles, with 100 Pt/Mo₂C showing HERactivity comparable to 20% Pt/C for the total ink volume.

As shown in FIG. 6(b) inset, at −144 mV overpotential 50 Pt/Mo₂Cproduced six times higher current than 20% Pt/C and two times higherthan 100 Pt/Mo₂C. It should be noted that LSV of 15 Pt/Mo₂C sample isnot presented since the Pt loading is under ICP-AES detection limit.Tafel plots of five catalysts are presented in FIG. 6(c), including Mo₂Cnanotube, 15 Pt/Mo₂C, 50 Pt/Mo₂C, and 100 Pt/Mo₂C as well ascommercially available 20% Pt/C samples.

Table 4 illustrates TAFEL slope and exchange current density of thevarious catalysts described herein

TABLE 4 Exchange Slope Current (−mV Potential Range Density (log(i₀)Sample vs. RHE) (−mV vs. RHE) (A cm⁻² _(disk))) 20% Pt/C −32 40-80 −3.62100 ALD cycle Pt/Mo₂C −34.7 40-80 −3.52  50 ALD cycle Pt/Mo₂C −33.140-80 −4.14  15 ALD cycle Pt/Mo₂C −59.7 120-300 −4.48 Bare Mo₂C −124150-400 −8.50

Tafel slope and exchange current density were calculated by fitting thelinear region of the plot in the following Tafel equation:

η=blogja

with η being the overpotential, j the current density, b the Tafel slopeand a the intercept of the plot. Exchange current density, j₀, wascalculated by setting overpotential η to zero using the above equation.The reported current densities (mA cm⁻²) in FIGS. 6(a), 6(b), and 6(c)are calculated using the disk area of the working electrode. Among thetested catalysts, Mo₂C has a slope of 124 mV/dec (FIG. 6(c) and Table4), suggesting that the HER follows the Volmer-Heyvorski mechanism(Volmer: H⁺+e⁻→H_(ad), Heyvorski: H_(ad)+H⁺+e⁻→H₂).

In contrast, all ALD Pt modified Mo₂C samples showed significantimprovement in HER activity relative to the unmodified Mo₂C.Specifically, the 100 Pt/Mo₂C samples demonstrated comparable slope andexchange current density to 20% Pt/C, while the 50 Pt/Mo₂C showed lowerHER activity than 20% Pt/C. The Tafel slopes of 50 Pt/Mo₂C and 100Pt/Mo₂C samples indicate that the HER follows the Volmer-Tafel mechanism(Volmer: H⁺+e⁻→H_(ad), Tafel: H_(ad)+H_(ad)→H₂), with therate-determining step being the hydrogen adsorption (the Tafel reactionstep). The Tafel slope of 15 Pt/Mo₂C indicates that the HER on the 15Pt/Mo₂C catalyst follows the Volmer-Heyvorski mechanism with theHeyvorski mechanism being the rate limiting step.

FIG. 7(a) illustrates cyclic voltammograms (CV) of 15 Pt/Mo₂C (Ptloading was below the detection limit of ICP or AAS) and bare Mo₂C. FIG.7(b) illustrates cyclic voltammograms of 50 Pt/Mo₂C (3.75 μg Pt cm⁻²_(disk)), 100 Pt/Mo₂C (15.4 μg Pt cm⁻² _(disk)), Pt/Mo₂C, and 20% Pt/C(70 μg Pt cm⁻² _(disk)) with a scan rate of 5 mV s⁻¹ in 0.5M H₂SO₄.Cyclic voltammetry (CV) of the 15 Pt/Mo₂C, 50 Pt/Mo₂C and 100 Pt/Mo₂Csamples was used to further characterize activity. FIG. 7(a) illustratesCV curves of Mo₂C and 15 Pt/Mo₂C catalysts with anodic current definedto be positive. The CV data was collected between −0.103 to 1.2 V vs.RHE for 15 Pt/Mo₂C and bare Mo₂C and −0.053 to 1.2V for samples withhigher Pt loading at scan rate of 5 mV s⁻¹. The 10th cycle isillustrated in FIG. 7(a).

It is contemplated that no Pt-like behavior was observed in the CV curvefor Mo₂C. In contrast, after 15 cycles of Pt ALD, CV of the modifiedMo₂C nanotubes (15 Pt/Mo₂C) demonstrated strong Pt-like features. Inaddition, the CV curve of Mo₂C showed an increase of anodic currentdensity from 0.1V (referred to as oxidation onset potential) andonwards. On the reverse scan, no reduction current was observed,indicating irreversible oxidation of the Mo₂C surface. Unexpectedly, the15 Pt/Mo₂C sample did not show any noticeable oxidation onset potentialin the entire voltage range (−0.103-1.2V), thus, demonstrating excellentstability towards oxidation with the atomic level Pt modification.

Comparison between the CV curves of 50 Pt/Mo₂C, 100 Pt/Mo₂C and 20% Pt/C(FIG. 7(b)) revealed similar HER onset potential and hydrogen oxidationpeaks, with 50 Pt/Mo₂C and 100 Pt/Mo₂C showing a single HOR peak currentdensity one and half and five times higher than commercially available20% Pt/C, respectively. The single HOR peak for 50 and 100 Pt/Mo₂C isconsistent with Pt (111) lattice spacing observed in FIG. 4, whilemultiple peaks were shown for 20% Pt/C sample with Pt beingpolycrystalline in phase.

To further characterize HER activity, Electrochemically Active SurfaceArea (ECSA) was calculated for hydrogen under potential adsorption(H_(upd)) region using CV curves in FIG. 7(b). ECSA for 50 Pt/Mo₂C and100 Pt/Mo₂C are 51.76 m² g⁻¹ and 40.52 m² g⁻¹ of Pt, which are 90% and49% higher than that of 20% Pt/C (27.25 m² g⁻¹ Pt), respectively. Giventhat 20% Pt/C has significantly higher BET surface area (158.59 m² g⁻¹catalyst) than 100 Pt/Mo₂C (25.68 m² g⁻¹ catalyst) and 50 Pt/Mo₂C (20.71m² g⁻¹), the higher ECSA value per Pt mass from Pt/Mo₂Cs indicates thatthe synergistic effect between the Pt and Mo₂C nanotube significantlyincreased the number of active sites. It is believed that the stronginteraction between Pt nanoparticle and Mo₂C nanotube support, asobserved in XPS BE shift and lattice spacing changes after depositing Ptnanoparticles, may have resulted in the increased oxidation stability.

Since the reaction rate of HER depends on hydrogen binding energy (HBE),it is believed that catalysts with the enhanced HBE provide for improvedhydrogen evolution reactivity. It is further believed that theenhancement in electrocatalytic activity in Pt ALD modified Mo₂Ccatalysts to the results from the electronic structure change. Thestrong interaction between both the Pt and the Mo₂C nanotube support,resulting from ALD deposition process, provides for improved hydrogenbinding energy (HBE).

Catalyst Durability

FIG. 8(a) illustrates durability tests with LSVs of 100 Pt/Mo₂C (11.9 μgPt cm⁻² _(disk)). FIG. 8(b) illustrates durability tests with LSVs of 50PT/Mo₂C (2.9 μg Pt cm⁻² _(disk)). FIG. 8(c) illustrates durability testswith LSVs of 20% Pt/C (54.3 μg Pt cm⁻² _(disk)). Each of FIGS. 8(a)-8(c)illustrate results before and after 48 hours of CPE at −69 mV. FIG. 8(d)illustrates 15 Pt/Mo₂C including the LSV after 3000 potential cyclesfrom −0.4 to 0.6V. The data of FIGS. 8(a)-(d) indicates a that 24%decrease in current density was observed for 20% Pt/C after 48 hours ofCPE, with no significant change for 50 Pt/Mo₂C and 100 Pt/Mo₂Ccatalysts. Interestingly, 15 Pt/Mo₂C had a 205% increase in currentdensity. Further analysis for 50 Pt/Mo₂C and 100 Pt/Mo₂C showed thatthere is a 3% increase for 50 Pt/Mo₂C, while 100 Pt/Mo₂C showed a 2.9%decrease.

FIG. 8(e) illustrates a graphical comparison of current density changeat −0.1V potential after 48 hours of CPE for each of catalysts 20% Pt/C,100 Pt/Mo₂C, 50 Pt/Mo₂C, and 15 Pt/Mo₂C. No further current densitydecay was observed for 50 Pt/Mo₂C, 100 Pt/Mo₂C and 20% Pt/C.Surprisingly, 15 Pt/Mo₂C exhibited an additional 225% increase incurrent density after the 3000 cycles of potential cycling (FIG. 8(d)).

Device Performance of Pt/Mo₂C Catalyst in PEMFC Anode

FIGS. 9(a)-(c) illustrate polarization and power density curve data ofMEAs fabricated with 100 Pt/Mo₂C and 20% Pt/C via brush painting sighSGL 10BC as the GDL (solid line 20% Pt/C; dashed line: 100 Pt/Mo₂Ccatalyst). The data represented in FIG. 9(a) utilizes an anode loadingof 0.02 mg Pt cm⁻². The data represented in FIG. 9(b) utilizes an anodeloading of 0.04 mg Pt cm⁻². The data represented in FIG. 9(c) utilizesan anode loading of 0.4 mg Pt cm⁻². The inset PCVs of FIGS. 9(a)-(c)refer to open circuit voltage. As illustrated in FIG. 9(a), 100 Pt/Mo₂Cexhibited higher open circuit voltage (OCV) (0.995V) than commerciallyavailable 20% Pt/C (0.939V) for Pt loading of 0.02 mg cm⁻². Currentdensity with 100 Pt/Mo₂C on the anode increased by 29.7%, while peakpower density increased by 48.6%.

For increased Pt loadings in FIG. 9(b) (0.04 mg cm⁻²) and 9(c) (0.4 mgcm⁻²), a similar OCV increase was observed in 100 Pt/Mo₂C (5.1%-6.6%).Current density and peak power density decreased for 100 Pt/Mo₂C forboth 0.04 and 0.4 mg Pt cm⁻², partially resulting from significantlylarger mass transfer resistance. Since 100 Pt/Mo₂C has 4.4% Pt massloading, to achieve same Pt loading for 100 Pt/Mo₂C and 20% Pt/C, aboutfive times total catalyst loading is applied on the GDL for 100 Pt/Mo₂C.For the same GDL area, the high total catalyst loading resulted in amuch thicker catalyst layer and, consequently, increased mass transferresistance. The higher open circuit potential for 100 Pt/Mo₂C indicatesthat 100 Pt/Mo₂C is more efficient than 20% Pt/C in generatingelectrons, which is consistent with the electrochemistry result shown inFIG. 6(b).

In summation, Pt nanoparticles of different sizes from three differentALD cycles can be successfully deposited onto phase-pure Mo₂C nanotube(atomic level for 15 ALD cycles, 2 nm for 50 ALD cycles, and 2.7 nm for100 ALD cycles). Moreover, the Pt nanoparticle size changes withdifferences lattice spacing, binding energy shift between deposited Ptparticles and Mo₂C nanotube support, HER activity and PEMFC anodeperformance of resultant catalysts. Specifically, two noticeable trendswere observed in lattice spacing: 1) Pt particles of 2.7 nm showedincreased lattice spacing from 0.21 nm to 0.24 nm; 2) those with a sizeof 2.0 nm have lattice spacing of 0.24 nm.

HER activity measurements and durability tests demonstrated that HERactivity and durability for all three Pt modified Mo₂C samples areimproved when compared to commercially available 20% Pt/C. In addition,excellent PEMFC anodic performance from 100 Pt/Mo₂C, relative to 20%Pt/C with low Pt loading (0.02 mg Pt cm⁻²) demonstrated that the Pt/Mo₂Cnanotube platform can be applied in a PEMFC anode or electrolyzer withfurther reduced Pt loading. It is also contemplated that the Pt/MO₂Cnanotube platform may be utilized in a PEMFC cathode. Still further, itis contemplated that various other transition metal carbide nanotubecatalyst system may be advantageously implemented in anodes or cathodesof a PEMFC. The combination of a rotatory ALD process and the uniquenanotube Mo₂C support morphology provides for precise fine-tuning of Ptnanoparticle size by adjusting the number of ALD cycles. The catalystsystems described herein serve as a pathway to further reduce Pt loadingwithout compromising durability.

While the foregoing is directed to embodiments of the presentdisclosure, other and further embodiments of the disclosure may bedevised without departing from the basic scope thereof, and the scopethereof is determined by the claims that follow.

What is claimed is:
 1. A catalyst formation method, comprising:preparing a mixture comprising one or more halide salts, multi-walledcarbon nanotubes, and a transition metal; heating the mixture to atemperature greater than about 900° C. to form a transition metalcarbide support; boiling and rinsing the transition metal carbidesupport to remove excess salts; drying the transition metal carbidesupport; depositing platinum (Pt) on the transition metal carbidesupport, wherein the depositing comprises atomic layer deposition (ALD)of platinum nanoparticles utilizing a platinum precursor and an oxygenprecursor in a rotating ALD reactor.
 2. The method of claim 1, whereinthe one or more halide salts are selected from the group consisting ofNaCl, LiCl, KCl, NaF, and KF.
 3. The method of claim 2, wherein the oneor more halide salts are NaCl and NaF.
 4. The method of claim 1, whereinthe transition metal is selected from the group consisting of Cr, Mo, W,V, Nb, Ta, Ti, Zr, and Hf.
 5. The method of claim 4, wherein thetransition metal is Mo.
 6. The method of claim 1, wherein the heatingthe mixture to a temperature greater than about 900° C. is performed fora period of time greater than about 10 hours.
 7. The method of claim 6,wherein the mixture is heated to greater than about 900° C. over aduration of about 9.75 hr.
 8. The method of claim 1, wherein thetransition metal carbide support is selected from the group consistingof chromium carbide, molybdenum carbide, tungsten carbide, vanadiumcarbide, niobium carbide, tantalum carbide, titanium carbide, zirconiumcarbide, and hafnium carbide.
 9. The method of claim 1, wherein thedrying the transition metal carbide support is dried in air at atemperature of between about 25° C. and about 100° C. for a period oftime between about 8 hours and about 16 hours.
 10. The method of claim1, wherein the depositing platinum is performed at a temperature ofbetween about 100° C. and about 300° C.
 11. A catalyst formation method,comprising: preparing a mixture comprising one or more halide salts,multi-walled carbon nanotubes (MWCNTs), and a transition metal, whereina ratio of halide salts:MWCNTs:transition metal is about 67:7:26;heating the mixture to a temperature greater than about 900° C. to forma transition metal carbide support; boiling and rinsing the transitionmetal carbide support to remove excess salts; drying the transitionmetal carbide support; depositing platinum (Pt) on the transition metalcarbide support, wherein the depositing comprises atomic layerdeposition (ALD) of platinum is performed in a rotating ALD reactor andthe number of ALD cycles is between about 15 and about
 100. 12. Themethod of claim 11, wherein the one or more halide salts are NaCl andNaF.
 13. The method of claim 11, wherein the transition metal is Mo. 14.The method of claim 11, wherein the Pt forms discrete Pt nanoparticleson the transition metal carbide support.
 15. The method of claim 14,wherein a diameter of the Pt nanoparticles on the transition metalcarbide support is less than about 3 nm.
 16. The method of claim 14,wherein the Pt deposition is performed for about 50 ALD cycles and adiameter of the Pt nanoparticles formed on the transition metal carbidesupport is about 1.5 nm.
 17. The method of claim 14, wherein the Ptdeposition is performed for about 100 ALD cycles and a diameter of thePt nanoparticles formed on the transition metal carbide support is about2.5 nm.
 18. The method of claim 11, wherein the transition metal carbidesupport comprises nanotubes having a length between about 1 micron andabout 2 microns and a diameter of between about 10 nm and about 15 nm.19. The method of claim 11, wherein the transition metal carbide supportcomprises phase pure molybdenum carbide nanotubes.
 20. A fuel cellapparatus, comprising: a proton exchange membrane; a first catalystcomprising platinum molybdenum carbide disposed on a first side of theproton exchange membrane, wherein the molybdenum carbide is phase pureand the platinum is formed as discrete nanoparticles on the molybdenumcarbide; a second catalyst comprising platinum molybdenum carbidedisposed on a second side of the proton exchange membrane opposite thefirst catalyst, wherein the molybdenum carbide is phase pure and theplatinum is formed as discrete nanoparticles on the molybdenum carbide;a first gas diffusion layer disposed on the first side of the protonexchange membrane, wherein the first catalyst is disposed between thefirst gas diffusion layer and the proton exchange membrane; a second gasdiffusion layer disposed on the second side of the proton exchangemembrane, wherein the second catalyst is disposed between the second gasdiffusion layer and the proton exchange membrane; an anode coupled tothe first gas diffusion layer; and a cathode coupled to the second gasdiffusion layer.